Classifications

• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
  • G05D16/00—Control of fluid pressure
  • G05D16/20—Control of fluid pressure characterised by the use of electric means
  • G05D16/2006—Control of fluid pressure characterised by the use of electric means with direct action of electric energy on controlling means
  • G05D16/2013—Control of fluid pressure characterised by the use of electric means with direct action of electric energy on controlling means using throttling means as controlling means
  • G05D16/202—Control of fluid pressure characterised by the use of electric means with direct action of electric energy on controlling means using throttling means as controlling means actuated by an electric motor
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S438/00—Semiconductor device manufacturing: process
  • Y10S438/909—Controlled atmosphere
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T137/00—Fluid handling
  • Y10T137/0318—Processes
  • Y10T137/0396—Involving pressure control
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T137/00—Fluid handling
  • Y10T137/2496—Self-proportioning or correlating systems
  • Y10T137/2559—Self-controlled branched flow systems
  • Y10T137/2564—Plural inflows
  • Y10T137/2572—One inflow supplements another
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T137/00—Fluid handling
  • Y10T137/7722—Line condition change responsive valves
  • Y10T137/7758—Pilot or servo controlled
  • Y10T137/7761—Electrically actuated valve

Definitions

• This invention relates to the field of 0 semiconductor wafer processing, and in particular to a method and apparatus for controlling the reaction chamber pressure in semiconductor wafer processing equipment .
• wafers are robotically transported into and out of a reaction chamber or process chamber where, under a controlled
• TCPTM 9400 single-wafer plasma etching system manufactured by Lam Research Corporation.
• Preprogrammed sets of process recipes are typically provided from the manufacturer. The operator may either select a programmed recipe or use an altered or customized recipe.
• RF power is delivered by a coil in the upper part of the reaction chamber and is tuned so as to ionize the process gases.
• RF power is also delivered to the wafer and is tuned so as to induce a DC bias on the wafer thereby controlling the direction and energy of ion bombardment of the wafer.
• An evacuation system continuously removes gases from the reaction chamber, and thereby maintains the desired pressure.
• the evacuation system typically comprises a turbo pump separated from the reaction chamber by a control gate valve.
• a pressure controller uses pressure data from a manometer in the reaction chamber to adjust the position of the control gate valve. The pressure controller opens and closes the gate valve to increase and decrease the vacuum supplied from the turbo pump to the reaction chamber. In this way, the pressure controller attempts to maintain the desired pressure in the reaction chamber as the gas flow rates into the reaction chamber vary from one process step to the next.
• the pressure controller compares the data from the reaction chamber manometer with the set point values programmed in the recipe. If either the process gas flow rate, or the desired pressure in the reaction chamber changes greatly from one process step to the next, the pressure controller may not be able to adjust the gate valve position appropriately. For example, if the next process step requires the gas to be introduced at much higher flow rates, the gate valve may initially over or under compensate, resulting in the wrong pressure in the reaction chamber at the beginning of the step.
• currently available systems perform a learn procedure each time a new recipe is used. The learn procedure creates a table of the approximate gate valve positions required for each process step in the new recipe. During the learn procedure, dummy wafers are processed according to the process steps of the recipe, and the controller notes the gate valve positions required for each step.
• Another problem with the currently available systems is related to the movement of the gate valve itself.
• a certain amount of waste material generated from the etching process collects on the surface of the gate valve.
• particulate matter is released in the surrounding environment. Due to the extremely low operating pressures, back diffusion may carry the particles back upstream to the reaction chamber, where undesirable contamination of the wafer may occur.
• transition time or stabilization time may sometimes be undesirably long.
• the transition or stabilization time is the time required to stabilize the pressure in the reaction chamber to the pressure set point for a processing step.
• the stabilization time typically takes around 20 seconds depending on the set point gas flow.
• chamber stabilization is achieved by introducing the process gases into the reaction chamber at the set point flow rates required by the next processing step.
• the stabilization time is often undesirably long.
• the present invention is directed to a method and apparatus wherein the pressure in the processing chamber is controlled by introducing a ballast gas into the evacuation system and the flow rate of ballast gas is adjusted according to the measured pressure in the processing chamber. Also in order to meet these objectives, the present invention is directed to a method and apparatus wherein the set point pressure and process gas flow are retrieved for a particular process step and the gate valve position is estimated by referencing gate valve position estimation curves stored in memory which correlate chamber pressures, gas flows, and gate valve positions.
• the present invention is directed to a method for raising the pressure in the processing chamber to the set point level wherein the process gas is initially introduced at a first predetermined flow rate which is higher than the set point flow rate, and after a predetermined amount of time or upon sensing of the pressure of the processing chamber approaching the set point level, the gas introduction rate is re-set to the set point level .
• FIG. 1 is a right side view showing some of the major assemblies of a wafer processing machine according to the present invention
• FIG. 2 is a schematic depicting a gas delivery system, reaction chamber, and evacuation system of a wafer processing machine according to the present invention
• FIG. 3 is a graph illustrating examples of stabilization times under prior art methods and according to the present invention
• FIG. 4 is block diagram illustrating some components of a control system and various interconnections between such components according to the present invention.
• FIG. 5 is a graph illustrating examples of gate valve position estimation curves according to the present invention.
• FIG. 1 A plasma etching system 100 is illustrated in FIG. 1, according to the present invention. It should be noted that the present invention is illustrated by way of example in FIGS. 1-2 as used with the TCPTM 9400 single-wafer plasma etching system manufactured by Lam Research Corporation. Based on the teaching set forth herein, a person of ordinary skill may readily utilize the present invention with any suitable vacuum or wafer processing equipment which requires control and manipulation of processing pressures in an evacuated environment.
• etching system 100 comprises an operator interface and control panel 102, from which the operators monitor and control the various processes and features of the etching system.
• Sender and receiver wafer indexers 104 send and receive wafers to and from the other processing assemblies in etching system 100.
• the wafers are robotically transported from the send indexer along the left side of the etching system to an entrance loadlock (not shown) . From the entrance loadlock, wafers are placed into the reaction chamber 106, where the plasma etching process takes place. Shown in FIG. 1 is the upper chamber housing 108, quartz window 110, and chamber manometer 112. After processing, the wafers enter the exit loadlock 114, and are transported back to indexers
• gas box 120 Also shown in FIG. 1 are gas box 120, plenum 122, gate valve 124, and turbo pump 126, all of which will be described in greater detail below.
• FIG. 2 illustrates, in schematic form, reaction chamber 106, gas delivery system 128, exhaust system 130, and control system 132.
• a wafer is placed or clamped on a lower electrode assembly within reaction chamber 106.
• reaction chamber 106 is kept under vacuum at all times except during maintenance.
• Exhaust system 130 serves to maintain this vacuum by evacuating gas from the reaction chamber.
• Gas delivery system 128 introduces process gasses into reaction chamber 106 through a gas ring 134, which comprises a plurality of gas outlets arranged in a ring about the lower electrode assembly and the wafer. Gas delivery system 128 is under the control of control system 132. Gas delivery system 128 supplies process gases to the reaction chamber via multiple gas flow paths which comprise manual shut-off valves 138, primary shut-off valves 140, mass-flow controllers 142, gas-mixing manifold 144. Although shown in FIG. 2 are four separate gas flow paths, in general any number of gas flow paths may be used according to the needs of a particular application. From gas-mixing manifold 144, the process gases pass through process gas line 146 and then into reaction chamber 106 via gas ring 134.
• Control system 132 directs gas panel interface 136 to open and close the mass-flow controllers 142 to regulate the flow of gases to the gas-mixing manifold 144.
• the control system would direct the mass flow controllers to simply set the flow of gases to the flow rate required by the next step.
• the speed of response is a strong function of the gas inflow rate.
• the stabilization time or transition time may advantageously be reduced by initially directing the mass-flow controllers to flow rates much greater than may be required for the next etching step.
• FIG. 3 shows examples of curves which illustrate the stabilization or transition time under the prior art method, 200, and the method according to the present invention, 202.
• the reaction chamber needs to be raised from only a few mTorr to a process step requiring 80 mTorr pressure and a set point flow rate of 40 SCCM.
• the gas is simply introduced at the set point of 40 SCCM, and the stabilization time is approximately 20 seconds .
• control system 132 which comprises host computer 180, bus 184, gas panel interface 13-6 and pressure controller 160.
• Host computer 180 is connected to a memory 182, which typically stores the process recipes in the form of a table of process steps, and the corresponding chamber pressures, process gas flow rates, RF power settings, gap spacings, and temperature settings for each process step.
• Bus 184 typically comprises a standard bus, such as VMEbus, which communicates with the host 180 via a local area network such as ethernet.
• Gas panel interface 136 communicates with the bus 184 typically via analog lines and D to A and A to D converters residing on bus 184.
• host 180 may set flow rates and read flow settings to and from mass flow controllers 142.
• mass flow controllers 142 are also controllable by pressure controller 160 via converters 188.
• Pressure controller 160 communicates with the bus 184 via RS232 connection or the like. Pressure controller 160 receives pressure readings from manometer 112, controls gate valve drive motor 162, and controls ballast gas mass flow controller 164a or 164b (explained in more detail below) .
• the increased inflow of process gas into the reaction chamber may be controlled by either pressure controller 160 or by host 180.
• pressure controller 160 controls the inflow of process gas
• pressure controller 160 sets the inflow to a high flow rate and monitors the pressure in reaction chamber 106 through chamber manometer 112.
• pressure controller 160 re-sets mass flow controllers 142 to introduce gas at the set point rate of the following process step.
• a suitable threshold pressure for re-setting the flow rates to the set point flow rate should be chosen for each particular configuration of equipment so that smooth coasting to the set point pressure is obtained. For example, it has been found on some machines that when the pressure is within about 10% of the set point pressure, the flow rate should be re-set to the set point flow rate.
• the host 810 may control the gas inflow rates via gas panel interface 136.
• the process gas is introduced at a high rate for a time t, after which the flow rates are re-set to the set point levels. It has been found that the proper time t, for changing the flow rate from the high level to the set point level, can be established through experiment, by running a dummy wafer through once and monitoring the time required to reach the set point pressure. The time t, may also be calculated by using a relationship that has been established through simple modeling of the chamber, as shown below:
• alpha varies with the particular configuration of equipment; a value of approximately 0.3 has been found for an experimental machine manufactured by Lam Research Corporation.
• the stabilization time and the transition time during pressure step changes may be significantly shortened, thereby making the process more efficient and increasing throughput.
• the evacuation system 130 serves to create a vacuum in the reaction chamber 106.
• Evacuation system 130 comprises plenum 122, gate valve 124, turbo pump 126, and ballast ports 150a and 150b.
• plenum 122 communicates directly with reaction chamber 106.
• gate valve 124 Between plenum 122 and turbo pump 126 is gate valve 124.
• valve 126 is shown and referred to as a gate valve, those of ordinary skill in the art will recognize that many alternative types of valves may be used which have a throttling effect on the flow of gas between the process chamber and the vacuum pump.
• Such valves include, for example, butterfly valves, vane-type valves, louvered-type valves, and iris-type valves.
• the evacuation system 130 may also comprise a backing pump (not shown) which is used to initially pump down reaction chamber 106 from atmospheric pressure to a rough vacuum pressure of about 1 mTorr.
• Control system 132 coordinates opening and closing isolation valves that connect each pump to the chamber so that turbo pump 126 continues to reduce pressure when the backing pump reaches its low pressure limit. Once the backing pump has pumped down the chamber to its low-pressure limit, turbo pump 126 is engaged to reduce the chamber pressure to less than 1 mTorr.
• ballast port 150a and ballast port 150b illustrate two alternative placements of a ballast port. Ballast port 150a is placed immediately upstream from gate valve 124; ballast port 150b is positioned downstream from gate valve 124 and inserts ballast gas directly into turbo pump 126. It is preferred that the placement of the ballast port be generally as far downstream as possible, to reduce the possibility of ballast gas back diffusing into the reaction chamber and interfering with the process.
• ballast gas may preferably be forced directly into one of the stages of the turbo pump, thereby greatly reducing the possibility of back diffusion. It is also preferable to use as a ballast gas a neutral gas such as nitrogen which may also be used for other purposes in the system operation or maintenance .
• the flow rate of the ballast gas is preferably controlled by a mass flow controller, under the direction of control system 132. Mass flow controllers 164a and 164b control the flow rate of ballast gas for ballast ports 150a and 150b respectively. As shown in FIG. 4, mass flow controllers 164a and 164b are controlled by pressure controller 160.
• ballast gas introduction may advantageously be used to increase the speed of response during pressure set point changes, as well as active control of the chamber pressure in place of the gate valve.
• the ballast gas introduction may precisely control the pressure in the chamber over a substantial range of operating pressures, advantageously reducing the need for gate valve position changes.
• the gate valve may be positioned in a few predetermined fixed positions, thereby extending the range of control by the ballast gas over the entire operating range of reaction chamber pressures. For example, it has been found in certain machines manufactured by Lam Research Corporation that using the ballast gas in combination with positioning the gate valve in three different positions, fully open, two- thirds closed, and fully closed, provides coverage of an adequate range of conductances for the evacuation system.
• a ballast gas may advantageously be introduced via a ballast port directly into or immediately upstream from the turbo pump, thereby effectively controlling the pressure of the reaction chamber without the need for adjusting the process gas inflow rate, or adjustments to the turbo pumping speed, and minimizing the amount of required movement of the gate valve.
• a number of conductance curves may be used to estimate the position of the gate valve for a given flow rate and pressure set point, thereby eliminating the need for performing a learn procedure whenever a change in set point pressure or flow is made for a particular step or whenever a new recipe is used.
• FIG. 5 illustrates examples of such gate valve estimation curves. In particular, a family of curves is shown, for various flow rates. It has been found that the curves tend to converge at high flow rates; in the case of FIG. 5, the curves tend to converge at flow rates above 100 SCCM.
• the preferred method of deriving the gate position estimation curves is as follows. For each flow rate, step through a sequence of gate valve positions and measure the resultant pressure for each position. The flow rate divided by the pressure measured is the conductance for that gate valve position. Repeat this process for each flow rate. It has been found that once the gate position estimation curves are derived, they remain accurate absent some drastic change in the turbo pump or the gate valve.
• the curves may be permanently stored in the memory of the control system.
• memory 190 is shown as part of pressure controller 160 and is preferably used to store the gate position estimation curves.
• the curves may be stored in memory 190 in the form of a matrix or array of values, or in the form of formulas or functions which have been fitted to the experimentally derived curves.
• Gate valves and controllers currently available typically operate in either pressure control mode or position control mode.
• pressure control mode the controller monitors the pressure in the chamber and tries to adjust the position of the gate valve to maintain the set pressure, while in position control mode the controller simply positions the gate valve to the set position.
• the gate valve should be operated initially in position control mode, with the position set point estimated from the gate position estimation curves stored in memory. For example, if the process set point is 20 mTorr pressure with 100 SCCM flow, the pressure controller estimates the gate position from the curve stored in memory. In the case of FIG. 5, the position would be approximately 380.
• the pressure controller is preferably switched to pressure control mode. For example, it has been found in some machines that when pressure controller is switched to pressure control mode when the pressure is within 5% of the set point pressure, smooth coasting to the set point pressure generally occurs.
• gate position estimation curves stored in memory advantageously eliminates the need to perform a new learn procedure whenever the pressure or flow set points are substantially altered for any of the process steps or whenever a new process recipe is used. Additionally, use of the estimation curves avoids the undesirable result of a learn procedure which is conducted while any of the gas supply valves or instruments are incorrectly tuned or calibrated.
• the gate valve position estimation curves may also be used when controlling the pressure using ballast gas.
• the gate valve In order to cover a wider range of conductances, the gate valve may be set in a small number of preselected positions.
• the gate valve estimation curves may be used to select -which gate valve position is best for a particular process step.
• a certain range of ballast flow is optimal for controlling the pressure in the reaction chamber. Assuming a ballast gas flow near the mid-point of the suitable range of ballast gas flow rates, adding that rate to the set point rate, and then dividing the combined flow rate by the set point pressure will yield a conductance value. This conductance value will indicate, when using the gate valve position estimation curves, which of the few preselected gate valve positions is appropriate.
• ballast gas flow is 0-300 SCCM for a given configuration
• the process gas flow set point is 50 SCCM
• chamber pressure set point is 15 mTorr.
• 150 SCCM the middle of the range of ballast gas, added to the set point flow and divided by the pressure yields a conductance of about 13.3 SCCM/mTorr.
• the ideal gate position would be about 500, and the nearest preselected position should be chosen. In the case of using three preselected gate positions, wide-open, fully closed, and two-thirds closed, the position of two-thirds closed would be chosen.

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• Physics & Mathematics (AREA)
• Fluid Mechanics (AREA)
• General Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Automation & Control Theory (AREA)
• Drying Of Semiconductors (AREA)
• Fluid-Driven Valves (AREA)
• Control Of Fluid Pressure (AREA)

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• 1996
  • 1996-03-29 US US08/627,711 patent/US5803107A/en not_active Expired - Lifetime
• 1997
  • 1997-03-27 JP JP53543397A patent/JP4417434B2/ja not_active Expired - Fee Related
  • 1997-03-27 WO PCT/US1997/005047 patent/WO1997037161A1/en active IP Right Grant
  • 1997-03-27 EP EP97917082A patent/EP0890050A4/en not_active Withdrawn

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